But there hasn't been much hard evidence on how much sleep children typically get, so a group led by Jessica Williams, a graduate student at the University of California Los Angeles, set out to get estimates of sleep times from birth to age 18. "These estimates are consistent with the amount of sleep recommended for children, and no evidence was found of racial/ethnic differences," the group wrote in its report.

The researchers gathered data from a nationwide survey that has tracked families for decades, focusing on parents' reports of their children's sleep, beginning in 1997. At that time, 2 832 children were included, in 2002 and 2007 the families were surveyed again and 2 520 and 1 424 children were included, respectively.

How the study was done

Williams's team found that until their second birthday, babies in the study slept an average of 12 to 14 hours during each 24-hour period. By age four it had dropped to about 11 hours of sleep and by age 10, to 10 hours. By age 16, kids were getting an average of about nine hours of sleep per night.

The US Centers for Disease Control and Prevention recommends that toddlers get 12 to 14 hours of sleep, preschoolers 11 to 13 hours, and adolescents aged 10 to 17 from 8.5 to 9.5 hours.

One of the big strengths of this study is that it tracked changes in sleep among the same children as they aged, said Maurice Ohayon, director of the Stanford Sleep Epidemiology Research Center in Palo Alto, California.

"We have an evolution of the sleep during the childhood. That is the unique thing," said Ohayon, who was not involved in the study.

The researchers didn't find any differences in the amount of sleep between boys and girls, and only a slight gap between white and Hispanic children.

Hispanic kids tended to sleep 19 minutes longer than white children after age nine, but Williams said that difference is too small to matter for individual kids.

Ask the Expert

Dr Alison Bentley is a general practitioner who has consulted in sleep medicine and sleep disorders, in both adults and children of all ages, for almost 30 years. She also researches and publishes on a number of sleep-related topics both in formal research journals and lay publications including as editor of Sleep Matters, an educational newsletter on sleep disorders for doctors.

posted on 02-12-2016

posted on 02-12-2016

posted on 02-12-2016

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